Background and Image color change

Question

Came across this webpage http://totallytransparent.tumblr.com/ Can anybody please tell me how this works? how does the background color and image color change/ match colors.

Answer 1

The background is an animated gif (http://static.tumblr.com/f13b0a6a22dd72346d930867ce349dff/zatppvx/DVQmt82k8/tumblr_static_colour-big.gif), the other images have transparent areas and the background "shines through".

Answer 2

It is just an .gif image used as background-image.

Url to the image: http://static.tumblr.com/f13b0a6a22dd72346d930867ce349dff/zatppvx/DVQmt82k8/tumblr_static_colour-big.gif